1. Technical Field
The disclosure relates to a device that stabilizes a workpiece during processing, and in particular to a device that stabilizes very thin semiconductor wafers or thin wafers for realizing a patterned rear side implantation of the thin wafer.
2. Background Information
For applications of electronic components, and in particular of integrated circuits (ICs) it is advantageous to restrict the total thickness of the integrated circuits or semiconductor circuits to a few micrometers. Such thin semiconductor circuits or semiconductor chips have a very small mass and a very small structural height, so they are of importance for many fields of application, such as in future disposable electronics and for chip cards and smart cards.
Such thin semiconductor circuits may be produced from so called thin wafers or ultra thin semiconductor wafers, semiconductor wafers of normal thickness with an initial thickness of approximately 500 to 1000 μm being thinned by grinding to a corresponding thickness after the production or a partial processing of respective semiconductor components.
However, since thicknesses of significantly less than 200 μm are desirable for future semiconductor components, and furthermore, in particular, two-sided processing may be required for forming semiconductor components processed on both sides, a significant problem in producing ultra thin semiconductor circuits consists in avoiding a fracture of the thin wafers or ultra thin semiconductor wafers.
Particularly in the production of new types of semiconductor components such as, e.g., light metal oxide semiconductor (MOS), insulated gate bipolar transistors (IGBTs), IGBT resistor-capacitor RC, or other devices, fundamental changes are required in the process sequences required in the processing of thin wafers. A central process in this so called thin wafer technology is a rear side processing of the thin wafer and in particular a rear side implantation for targeted setting of electrical parameters for the finished component or the final semiconductor circuit.
Two problems, in particular, may occur during the implantation of thin wafers or ultra thin semiconductor wafers using apparatuses that have been commercially available heretofore. The mechanical stability, in particular an edge stability of the thin wafers, is so low that in the case of apparatuses based on a rotation principle, on account of the centrifugal forces that result, wafer fractures or instances of wafer edge damage occur to an increased extent. These result essentially from the mechanical edge loading and the mechanical wafer holding devices. Secondly, the thin wafers, in particular at the stage of a high degree of r processing, that is to say that the semiconductor circuit is almost completed, form such a bow that in the case of implantation apparatuses based on electrostatic holding devices, it is not possible to ensure sufficient adhesion during the implantation.
Furthermore, there is increasingly the need for a patterned processing and in particular for a patterned implantation, in particular, of a rear side of the thin wafer in which only specific regions of the semiconductor wafer are processed or implanted.
Conventional devices and methods for carrying out a patterned processing of semiconductor wafers are generally known, in particular in the processing of wafers of normal thickness or so called thick wafers. In this case, a layer of photoresist is applied on the semiconductor wafer and the regions to be processed or implanted are uncovered by a photolithographic patterning. After the processing or implantation, the photoresist is removed again by wet chemical and/or dry chemical means. A conventional method of this type brings about a large number of problems, however, in the case of thin wafers and in particular when using very high implantation doses of >1·10^15/cm2.
The number of process steps and the associated additional handling of the thin wafers are significantly increased because of the photolithographic patterning used. Consequently, at least four process steps are required for a conventional photopatterning (resist coating, exposure, development, resist stripping), and further process steps such as e.g. inspection, or resist curing may possibly be added. Experience shows that each additional process step, particularly in the case of thin wafer technology, leads to increased edge damage and ultimately to wafer fracture.
Furthermore, in particular during implantation with very high doses of >1·10^15/cm2, on account of thermal and chemical conversion processes of the photoresist as a result of the bulk implantation, considerable problems arise in removing the so called “cracked” photoresist again from the surface of the thin wafer, for which reason at the present time recourse is had to the so called “double resist technique”, in which two or more layers of photoresist are used so that the photoresist layer which is applied directly to the silicon wafer is protected against the “harmful” influence of the implantation and is obtained such that it can be removed by the abovementioned methods (wet chemical and/or dry chemical etching process).